Summer caulis are much sweeter than winter ones if you can grow them (I can't). There is a summer version of purple sprouting broccoli and kale can be picked in the summer too. Radishes are a brassica, as is Kohl Rabi. There are various Chinese brassicas such as mizuna, Chinese cabbage (Chinese leaves) and pak choi. Red cabbage is wonderfully satisfying to grow but we have found that the cabbages 'blow' very suddenly, so maybe sow them in succession rather than starting them all off at once.